<!doctype html>
<html>
<head>
    <meta charset="UTF-8">
    <title>三角形</title>
    <link rel="stylesheet" href="css/border.css">
</head>
<body>

  <div class="netease-nav">
       <div class="logo"></div>
       <ul>
           <li class="active">首页</li>
           <li>电影<div class="arrow"></div></li>
           <li>影院</li>
           <li>客户端</li>
       </ul>
  </div>

  <div class="wp">
      <div class="red-btn">点我弹出/隐藏弹出框</div>
      <div class="pop-hover">
          <div class="arrow2"></div>
          <div class="arrow3"></div>
      </div>
  </div>
</body>
</html>